The present invention relates to wireless power supplies, and more particularly to wireless power supplies with integrated data communications.
There is an increased effort in the market to develop wireless power supply systems capable of charging and/or powering a wide variety of electronic devices. Wireless power supply systems allow power to be delivered to an electronic device without the need for direct-wired connections. This eliminates a variety of problems associated with direct electrical connections, such as the mess and clutter associated with cords as well as the inconvenience associated with repeatedly plugging in and disconnecting charging cords from portable electronic devices.
Many conventional wireless power supply systems rely on inductive power transfer (i.e. the transfer of power using electromagnetic fields) to convey electrical power without wires. A typical inductive power transfer system includes an inductive power supply that uses a primary coil to wirelessly transfer energy in the form of a varying electromagnetic field and a remote device that uses a secondary coil to convert the energy in the electromagnetic field into electrical power. Recognizing the potential benefits, some developers have focused on producing wireless power supply systems with adaptive control systems capable of adapting to maximize efficiency and provide appropriate operation to a variety of different types of devices under a wide range of circumstances. Adaptive control systems may vary operating parameters, such as resonant frequency, operating frequency, rail voltage or duty cycle, to supply the appropriate amount of power and to adjust to various operating conditions. For example, it may be desirable to vary the operating parameters of the wireless power supply based on the number of electronic device(s), the general power requirements of the electronic device(s) and the instantaneous power needs of the electronic device(s). As another example, the distance, location and orientation of the electronic device(s) with respect to the primary coil may affect the efficiency of the power transfer, and variations in operating parameters may be used to optimize operation. In a further example, the presence of parasitic metal in range of the wireless power supply may affect performance or present other undesirable issues. The adaptive control system may respond to the presence of parasitic metal by adjusting operating parameters or shutting down the power supply. In addition to these examples, those skilled in the field will recognize additional benefits from the use of an adaptive control system.
A number of adaptive control systems rely on data communication between the adaptive control system (sometimes referred to as the “primary-side”) and the portable electronic device (sometimes referred to as the “secondary-side”). For example, the adaptive control system and the portable electronic device may perform a handshake or otherwise communicate to establish that the portable device is compatible with the wireless power supply. The portable device may also communicate its general power requirements, as well as information representative of the amount of power it is receiving from the wireless power supply. This information may allow the adaptive control system to adjust its operating parameters to supply the appropriate amount of power at optimum efficiency. These and other benefits may result from the existence of a communication channel from the electronic device to the wireless power supply.
To avoid the need for additional communications systems, some existing inductive power supply systems transmit data communications over the existing inductive coupling. For example, the electronic device may include a secondary-side controller that sends communications to the adaptive control system using “backscatter modulation,” which places the communications onto the power signal. In this type of system, the secondary-side controller modulates the amount of power that the electronic device draws from the wireless power supply, thereby establishing communications using amplitude modulation of the power signal. In some applications, modulation of the amount of power drawn by the electronic device is achieved by toggling a load on the secondary-side, such as a dedicated load resistor.
At least one existing wireless power supply system uses a current sensor in the primary-side tank circuit to monitor current in the power signal to extract the data communications from the power signal. Although this technique works well and is highly reliable, it may be possible to provide improved reliability in some circumstances. For example, the signal-to-noise ratio inherent in this existing technique may be relatively low in some applications, thereby making it more difficult to discriminate between data and noise.